This invention relates to a method of and an apparatus for producing an exposure mask.
An exposure mask such as a photo-mask which is used to produce a semiconductor device is produced, for example, in the following manner.
FIG. 5 illustrates in flow chart an outline of a process of producing an electron beam (EB) file in a method of producing an exposure mask.
Referring to FIG. 5, using an LSI designing CAD (computer aided design) apparatus, a designer first performs LSI designing to produce LSI pattern data (hereinafter referred to also as layout data) in accordance with an exposure mask to be produced.
Then, graphic form calculation is performed for the layout data (step S1) and pattern correction (step S2) is performed if necessary, and then EB conversion is performed (step S3) to produce an EB file 2 which is an input format for an EB plotting apparatus.
However, when an exposure mask for production of a semiconductor device which includes repetitions of a same pattern such as, for example, a memory device is to be produced, if it is tried to produce the entire mask in a batch in accordance with the procedure illustrated in FIG. 5, then a large number of same patterns are produced at different positions. This is low in the efficiency. Further, it sometimes occurs that data regarding specifications for an exposure mask are required separately.
Division Processing of Layout Data
Another method is available wherein, for example, as seen from FIG. 6, layout data are divided for individual repetitive regions and a procedure same as that illustrated in FIG. 5 is applied to each of the thus divided layout data.
In the method just described, it must be indicated how to divide layout data. The indication may be given by a method wherein coordinate values of an area to be produced by division are designated or another method wherein the name of any of cells which compose layout data (layout data are normally designed hierarchically, and each of such hierarchies is called cell) is designated.
In the method illustrated in FIG. 6, layout data 10 are divided (step S10), and one of processes in steps S12, S13 and S14 is selectively performed for each of the plurality of data obtained by the division in accordance with conditions to produce EB files 12, 13 and 14, respectively. Further, a job file (hereinafter referred to also as plotting job) 11 which designates arrangements and/or repetitions necessary for the EB files 12, 13 and 14 is produced (step S11) to re-construct the entire mask image.
However, the operation for dividing the layout data 10 (step S10) and the operation for producing the plotting job 11 (step S11) rely much upon manual operation and make a bottle neck to the process of production of an exposure mask.
Further, where an exposure mask to be produced locally has, for convenience in layout designing, an area in which a different processing method for graphic form calculation is to be performed or another area in which a different correction method is performed, since batch processing based on the procedure illustrated in FIG. 5 is impossible, the layout data are divided into portions for which different processes should be performed and are processed in accordance with the procedure illustrated in FIG. 6.
Also in this instance, an indication for such division may be given by a method wherein coordinate values of the areas are designated or another method wherein names of cells which compose the layout data are designated, and this gives rise to the problem described above.
Further, layout data may be processed dividing them into portions for which different quantization steps are used.
In particular, upon EB conversion, coordinate values of pattern data are quantized into minimum units which are handled by a plotting apparatus. Generally in layout designing, a design grid is selected so that rounding of coordinate values may not occur in such quantization to produce pattern data.
However, when it is intended to shrink already designed pattern data to produce a mask or when there are layout data which include a partially different design grid, in order to prevent rounding of a pattern upon quantization of EB conversion, the plotting unit dimension of the plotting apparatus (where an electron beam plotting apparatus of the raster scanning type is employed, such processing as to partially vary the plotting unit dimension is called spot size) on the same mask to set the individual quantization units to such varies with which no rounding occurs.
Also in such an instance as just described, processing is performed in accordance with the procedure illustrated in FIG. 6, in which portions having different quantization dimensions are processed after division processing is performed. Therefore, the problem described above arises similarly.
Inspection of an Exposure Mask
An exposure mask produced is normally inspected using a defect inspection apparatus and is shipped after it is guaranteed that it is free from a defect or does not have a defect of a certain fixed level.
Consequently, where a plurality of same LSI chip patterns (hereinafter referred to chips) are present on the exposure mask, two methods are available including a method wherein coordinate values of rectangular areas occupied by the chips and information that the patterns of the chips are same as each other are indicated to the defect inspection apparatus to indicate it to the defect inspection apparatus to perform comparison inspection between the patterns of the areas and another method wherein coordinate values of the rectangular areas other than a rectangular area of an object of inspection by visual observation are indicated to indicate it to the defect inspection apparatus to perform comparison inspection with pattern data used for plotting based on an EB file (for example, an EB file or EB files and a plotting job).
Also a case exists wherein defect inspection with a defect inspection apparatus is not performed correctly due to presence of a special pattern in an area designated as an object of inspection. This is a case wherein, generally where a pattern on data is excessively small with respect to the inspection capacity (accuracy) of the defect inspection apparatus or to the capacity (pattern formation accuracy) of the mask production process, a false defect is detected.
Where such a situation as described above is known in advance, the area is designated as a non-object area of defect inspection also in coordinate values of a rectangular area.
While such area coordinate values depend upon patterns on layout data, the data are delivered using another medium different from the layout data such as a different file on a computer or paper.
Therefore, as an operation for such data delivery, an operator must read the coordinate values from the layout data. Here, there is the possibility that an artificial reading error may occur. Further, since the thus read data are copied to another medium, also a mistake in copying may possibly occur.
Accuracy Guarantee of Exposure Mask
As a method of guaranteeing the accuracy of the exposure mask produced, in addition to the defect inspection described above, the dimensions of the detailed patterns on the produced exposure mask are measured and it is measured whether the dimensions on the data remain within tolerances corresponding to the required accuracy to guarantee the accuracy in dimension of the patterns on the exposure mask.
Here, it is necessary to measure any pattern on the exposure mask and deliver as data what are the detailed dimensions of the pattern.
While also those data depend upon the pattern on the layout similarly to the area data for defect inspection described above, as a delivery method therefor, the data are delivered in the form of a medium different from the layout data such as another file on a computer or paper.
Accordingly, similarly as in the case of the defect inspection described above, there is the possibility that a miss by an operation by a person may occur.
Specifications of Exposure Mask
Data regarding specifications of a mask other than those described above such as a material to be used for the production of the mask, the thickness, size and accuracy of the mask, and a name to be indicated on the mask are not included in the layout data.
Therefore, such data are delivered using some medium such as paper. Consequently, when the data are delivered, or when, after such data are delivered, data of a plurality of media are confirmed and necessary processing is performed, a miss by the operator may possibly occur.
Furthermore, if a plurality of media which describe mask specifications are present, then there is the possibility that data on the media may be mistaken for data for another mask or any of the media may be mistaken for another file on a computer or some other paper such as specification paper.
Where, in a process of production of an exposure mask, an operation for dividing layout data, indication of data for inspection of the exposure mask, indication of data for accuracy guarantee of the exposure mask and management of specification papers for the exposure mask are performed manually by a designer or an operator as in the procedure described hereinabove with reference to FIG. 6, the production process for the exposure mask is interrupted. Consequently, there is a problem in that the period required for the production of the exposure mask is increased accordingly and there is a high degree of possibility that a miss by a person may occur.
It is an object of the present invention to provide a production method and apparatus for an exposure mask by which an exposure mask can be produced in a reduced production period and with a high degree of reliability.
In order to attain the object described above, according to an aspect of the present invention, there is provided a method of producing an exposure mask, comprising the steps of retrieving, from layout data, indication data which indicate a data process which does not have an influence on a pattern itself of an exposure mask and include a predetermined index code, producing a file based on the retrieved indication data, performing the data process based on the file and processing the layout data with the processed data to produce a pattern file and a plotting job, and performing plotting based on the pattern file and the plotting job to produce an exposure mask.
The pattern file is, for example, an EB file where plotting is performed using an electron beam (EB). In the present specification, since it is described that plotting is performed by using an EB, the pattern file is referred to as EB file. Naturally, however, plotting may be performed not using an EB but using a laser beam.
The data process is, for example, a process for dividing the layout data in accordance with a processing condition. In this instance, the layout data divided based on the file and processed are unified to produce the plotting job.
In particular, in the step of production of layout data, a designer places, in accordance with the necessity, indication data which indicate a data process which does not have an influence on a pattern itself of an exposure mask into the layout data. For example, the designer places, for example, into a definition of a cell, indication data indicating that the layout data regarding the cell should be divided and processed in accordance with a processing condition.
Then, from the layout data, the indication data are automatically retrieved, for example, by a system, and the layout data regarding the cell are divided in accordance with the thus retrieved indication data and processed. Further, contents of the indication data are stored into a single file.
At a next stage in which a plotting job is to be produced, the divided and processed layout data are unified based on the file to produce the plotting job.
According to another aspect of the present invention, there is provided an apparatus for producing an exposure mask wherein plotting is performed based on a plotting job produced from layout data to produce an exposure mask, comprising retrieval means for retrieving, from the layout data, indication data which indicate a data process which does not have an influence on a pattern itself of an exposure mask and include a predetermined index code, file production means for producing a file based on the retrieved indication data, data processing means for performing the data process based on the file, and means for producing a pattern file and a plotting job from the layout data based on the data processed by said data processing means.
With the method of and apparatus for producing an exposure mask, the period for production of an exposure mask can be reduced and the reliability in the process of production of an exposure can be improved.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols.